How is baryonic matter estimated @ 5% of the Universe volume?

Question

Where simple calculation shows its volume to be 1.4 x10^-76 per cent of the geometrical volume of the Universe?

Answer 1

Hi goring

The baryonic matter estimates are at % of mass (or, more properly, contribution to mass-energy density). The most recent observations indicate the following:

* about 70% of the energy density of the universe is dark energy (for physicists this is an omega value of 0.7, where omega is the ratio of the actual density to the critical flatness density)

* about 30% (omega = 0.3) of the energy density is normal mass-energy

* of this 30%, about 27% is dark matter, and the remaining 3% is baryonic or luminous matter

* about 20% of the total dark matter mass is likely to be massive neutrinos (small weakly interacting particles), about 10% large non-luminous objects (eg black holes, neutron stars, brown drawfs, etc) and the remainder unsure as yet

* of the baryonic matter the vast majority is hydrogen, followed by helium, and then (relative) traces of other elements.

As you suggest, the size of a hydrogen nucleus (a proton) is particularly small. So if you saw a statement to the effect that baryonic matter makes up 5% of the universe by volume, then that statement is wrong. However 5% of the mass-energy density is in the right ballpark.


Hope this helps!
The Chicken